Effect of acute pretreatment of lead on picrotoxin-induced convulsions in rats.

The effect of acute exposure to lead acetate (LA)/lead nitrate (LN) on onset and severity of convulsions induced by a low dose of picrotoxin was examined in rats. Both LA and LN reduced the time of onset and exacerbated the severity of convulsions, with a resultant high lethality. On comparison, it was noted that in the LA-pretreated group, convulsion scores and incidence of tonus and mortality were much higher; the appearance of tonus was more delayed than in the LN-pretreated group. In lead-pretreated animals, the potentiation of picrotoxin-induced convulsions was accompanied by higher lead levels in blood (p < 0.001). However, the whole-brain lead levels were not significantly different in these animals compared to the controls. The difference in the degree of potentiation by the two forms of lead could possibly be attributed either to the role of a combination of anions and cations or to the variable cerebral uptake and regional distribution of lead or due partly to the extent of competitive interaction involving d-aminolaevulinic acid--whose level is known to be elevated consequent to lead-induced disruption of haem biosynthesis--at GABA receptors.